Dejan B.

Dejan B.

Mentor
5.0
(480 reviews)
US$25.00
For every 15 mins
693
Sessions/Jobs
ABOUT ME
FULL REFUND if I can't help! Leetcode Interview preparation FAANG, Algorithms expert, System design, C++, Python, Java, Machine learning, AI
FULL REFUND if I can't help! Leetcode Interview preparation FAANG, Algorithms expert, System design, C++, Python, Java, Machine learning, AI

Winner of multiple algorithm contests, with 14 years of IT experience. I have a Masters degree in AI & Machine learning. I can prepare you for interviews or exams, by creating a study plan, based on your skills, just for you.

I was told by multiple clients, after they chatted with multiple algorithm mentors here, seeking assistance for implementing or explaining some advanced complex algorithm/data structure, either everyone turned them down, or those mentors refunded their money after wasting them few hours or days.
At the end I was the only person that could help them with more advanced topic.
That is why I am asking for relatively higher price than others.
You can contact any of my previous clients, in my reviews, and ask them yourself about me.

https://leetcode.com/dejandenib/

Here is a scan of my diploma Master in Artificial Intelligence:
https://drive.google.com/file/d/1bWXKgUsgcLUwGarpB7aeou7iE-jHGGHQ/

Here I am on the news, for winning the most prestigious algorithm national contest:
https://web.archive.org/web/20220508204135/https://www.netcetera.com/home/stories/news/20140616_codefu.html

Feel free to message me and request proof of any other credentials.

My biggest strengths are:

  • Mentoring people who prepare for coding interviews
  • Designing algorithms and data structures (like Leetcode/Hackerrank/Codility)
  • Machine learning, reinforcement learning, data science, computer vision

My Master thesis was creating a game agent that plays the FPS video game Doom, using deep reinforcement learning.
I've done a lot of competitive programming, like Hackerrank, Topcoder, International Olympiad in Informatics, ICPC-ACM, Google Codejam and Hashcode.

I was awarded full scholarships all throughout my high school, Bachelor, and Master studies, for my excellent grades and contests performance.
On my Bachelor in Computer Science, I graduated among top 5% in generation.
For my Master in Artificial Intelligence in Netherlands, I was the only student awarded with a full scholarship.

My work experience:

  • At the moment I am working on my own e-commerce startup. I developed the backend using Django, created a smart search engine, which pushed my algorithm and data structure knowledge to the limits. I also develop an image recognition system, with computer vision and deep learning, to be able to take a photo of some product in front of you, and the website immediately gives you the wanted product.
  • I've done a lot of mentoring and teaching to high school and university students, for algorithm and math exams, as well as preparing them for algorithm contests. I also mentored many junior colleagues at work as well as making presentations in front of the whole company, in the field of machine learning.
  • I worked at Tabtale, a mobile game development company from Israel. Used the Cocos 2D game engine in C++, programmed for Android with Java and for iOS with Objective-C.
  • Worked in Maxwell Biosystems, startup based as part of ETH-Zurich University in Switzerland. I was doing data science analysis in Python and Matlab, on neuron recordings.
  • Worked remotely for a data science startup Slovenia, on various projects: mentoring data science interns, churn prediction in telecom sector, bus arrivals predictions, predicting gamer playing style in a multiplayer game and matching players in teams based on their rank and playing style.
  • I was a teaching assistant at university, for the course Advanced Algorithms
    Just message me to find out more about me! :)
English
Eastern Time (US & Canada) (-05:00)
Joined May 2020
EXPERTISE
13 years experience | 162 endorsements
Experience from tutoring, mentoring, teaching students and colleagues, and my personal experience from interviews.
Experience from tutoring, mentoring, teaching students and colleagues, and my personal experience from interviews.
14 years experience | 153 endorsements
Experience with algorithm programming contests: Gold Medal in my country. Bronze medal on the Balkan (South European) Olympiad in Informa...
Experience with algorithm programming contests: Gold Medal in my country. Bronze medal on the Balkan (South European) Olympiad in Informatics.
C++JavaPython
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C++JavaPython
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14 years experience | 108 endorsements
C++JavaPython
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10 years experience | 15 endorsements
Worked as a teaching assistant at university, and held many private classes, to individuals and groups
Worked as a teaching assistant at university, and held many private classes, to individuals and groups
5 years experience | 2 endorsements
Did my Master in Artificial Intelligence and worked in data science companies
Did my Master in Artificial Intelligence and worked in data science companies
7 years experience | 36 endorsements
Many University and work projects, at different companies and domains
Many University and work projects, at different companies and domains
13 years experience | 8 endorsements
Used C++ for algorithms and data structures, aplication GUIs, creating a game and AI agent to play against, used it in Cocos game engine ...
Used C++ for algorithms and data structures, aplication GUIs, creating a game and AI agent to play against, used it in Cocos game engine and many other projects

REVIEWS FROM CLIENTS

5.0
(480 reviews)
Anjali M
Anjali M
December 2025
Dejan did a great job guiding me on how to prepare for Leetcode interviews. He gave me strategies to improve and shared how he was able to solve all types of questions.
Karina Makhani
Karina Makhani
November 2025
Dejan was really nice, the content we went over was helpful and I appreciated his emphasis on communication in interviews!
Mo Gedi
Mo Gedi
November 2025
I had an excellent system design session with Dejan today. He broke down the core principles of approaching system design interviews in a way that clicked for me. We discussed how to structure answers under time pressure, what common pitfalls to avoid, and how to prioritize clarity over complexity. Dejan also helped me identify which areas I should focus on next. We even dug into how one might architect something like YouTube, which made the concepts feel much more real and applicable. He’s clearly deeply knowledgeable, but just as importantly, he knows how to explain things in a digestible and actionable way. Highly recommended if you’re serious about leveling up your system design skills.
Rikki W
Rikki W
November 2025
I struggled a lot with Leetcode and Dejan showed me how to study better and more efficiently. He showed me my gaps of understanding and gave me home practice to make the most of the sessions. He teaches really deep concepts but makes them easy to understand.
Dylan Martin
Dylan Martin
October 2025
Does a phenomenal job at breaking down problems into more digestible pieces and explaining the reasoning behind solutions.
Tina
Tina
September 2025
Dejan is professional and honest, I wanted real advice on how to improve my technical interview skills and he provided me his honest advice from his wealth of experience.
Jiani Zhou
Jiani Zhou
September 2025
Dejan was one of the best mentors I have ever seen! He has a lot of experience in competitions, and he is really kind! Dejan showed me some key mistakes in my coding experience, and helped me greatly. I would recommend him to any person in need of some coding help.
Roman Kulakov
Roman Kulakov
June 2025
I sought Dejan to learn about Algorithms and CS questions that may come up in the upcoming interview he showed me some really outside of the box kind of details of the data structures that I thought that I knew. Would recommend!
James tractenberg
James tractenberg
June 2025
My session with Dejan went great. Dejan is very patient and helpful. He really understands the underlying concepts of DSA and prepared me very well for my interview. He not only teaches the concepts for interviews but also how to communicate effectively in interviews.
Kanaan Abukhadra
Kanaan Abukhadra
May 2025
He's skilled at what he does. Highly recommend!
EMPLOYMENTS
Mock interviewer
Codementor
2015-08-01-Present
Helped many students, and full time developers, with mock interviews for algorithm design problems, and how to study and prepare for them.
Helped many students, and full time developers, with mock interviews for algorithm design problems, and how to study and prepare for them.
Python
Java
C++
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Python
Java
C++
Algorithm
Data structure
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Data Scientist
A3S-Delta Slovenia
2019-03-01-2019-12-01
I worked on different projects during my collaboration with this company: Mentoring data science interns, with Scikit learn, for a city b...
I worked on different projects during my collaboration with this company: Mentoring data science interns, with Scikit learn, for a city bus schedule arrivals prediction. Team lead, gathering client requirements, predicting gamer playing style in a multiplayer game and matching players in teams based on their rank and playing style, with Python. Data Science onsite consultant, customer churn analysis for the company Du telecommunications, based in Dubai, United Arab Emirates, with Rapidminer
Python
NumPy
Weka
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Python
NumPy
Weka
TensorFlow
RapidMiner
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Machine learning Engineer
Maxwell Biosystems in Switzerland
2017-08-01-2017-12-01
Maxwell Biosystems is a startup, as part of University ETH-Zurich, ranked top 5 in the world for engineering. I did a 1 semester, 5 month...
Maxwell Biosystems is a startup, as part of University ETH-Zurich, ranked top 5 in the world for engineering. I did a 1 semester, 5 month internship, as part of my Master studies. My work as a data scientist was machine learning for feature classification & analysis of neuron activity in MATLAB & Python
Python
NumPy
MATLAB
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Python
NumPy
MATLAB
TensorFlow
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PROJECTS
Game playing AI agent, for the video game Doom, with Deep reinforcement learning and A3C
2018
This was my Master thesis. The game agent uses raw visual input, and from the pixels with OpenCV, decides the next action. Compared diffe...
This was my Master thesis. The game agent uses raw visual input, and from the pixels with OpenCV, decides the next action. Compared different algorithms: Deep reinforcement learning with improvements, and A3C. This was developed in Tensorflow with Python Used the VizDoom platform for testing. Training the agent was done on AWS cloud.
Python
OpenCV
TensorFlow
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Python
OpenCV
TensorFlow
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AI playing checkers
2016
As a University project, and motivated by my love for playing the board game Checkers, I implemented AI agent to play the game. Developed...
As a University project, and motivated by my love for playing the board game Checkers, I implemented AI agent to play the game. Developed it with Visual C++ in Visual Studio 2015. Didn't use any deep learning, but traditional chess playing techniques, like alpha beta minimax negamax search, hashing of game states for faster search
C++
Visual Studio
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C++
Visual Studio
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